1. Field of the Invention
This invention relates to an optical fibre and has particular but not exclusive application to use as an optical amplifier.
2. Related Art
It is known that erbium doped fibres can be used as optical amplifiers. However, they suffer from a number of disadvantages. For example, a long length of fibre is required in order to achieve a significant level of amplification, e.g. 10 m. Also, erbium is a toxic substance so manufacture of the doped fibre is complex and requires strict pollution control measures.
Recently, it has been shown that very small particles, fabricated on the nanometre scale, give rise to specific optical effects, such as electroluminescence. A review is given in Colloidal Semi-conductor Q-Particles; Chemistry in the Transition Region Between Solid State and Molecules, M. Weller: Angew, Chem. Int. Ed. Engl. 1993, 32,41-53. These nanometre scale particles are known as quantum dots.
A laser making use of quantum dots is described in U.S. Pat. No. 5,260,957. In this arrangement, a host material such as PMMA contains quantum dots. The laser may be in the form of a channel waveguide device, the host material being arranged in a cavity formed in a channel machined in a substrate, the substrate having a lower refractive index than the host. The laser is pumped by an external light source in order to provide a laser output. The use of polymeric material is said to be advantageous.
An optical fibre with non-linear optical characteristics is known from JP-A-4-195028, in which the interior of a tubular glass sheath is coated with materials that, on subsequent heating, form particulate material disposed in a glass core of the fibre.